Conversion of hydrocarbons



C. G. DRYER ET AL CONVERSION oF HYDROCARBONS Filed July 30, 1941 jldv@www

Sept. 28, 1943.

'Patented Sept. 28, 1943 CONVERSION OF HYDROCARBONS Charles G. Dryer andRalph B. Thompson, Chicago, Ill., assignors to Universal Oil ProductsCompany, Chicago, Ill., a corporation of Dela- Ware Application July 30,1941, Serial N0. 404,604

14 Claims.

This invention relates to the conversion of hydrocarbons and moreparticularly to the treatment of natural gasoline or other substantiallyparalnlc hydrocarbon distillates.

One of the major problems confronting the petroleum industry at thepresent time is the marketing of the large quantity of natural gasolineavailable. The natural gasoline usually is of an acceptable octane valuebut is of such high vapor pressure that it cannot satisfactorily be usedfor motor fuel as originally recovered, When the natural gasoline isstabilized to reduce it to an acceptable vapor pressure, not only is asubstantial portion of the gasoline discarded, but the gasoline isreduced to such a low octane value that it is not satisfactory for useas a motor fuel. 'It is, therefore, an object of this invention toprovide suitable means of converting the large supply of naturalgasoline into satisfactory motor fuel.

The present invention provides a method whereby the vapor pressure ofnatural gasoline or similar gasoline may be reduced to an acceptablevalue, while at the same time the octane value is either maintained orincreased, while a minimum amount of the hydrocarbons is discarded fromthe gasoline. This is accomplished in accordance with the presentinvention by means of a series of cooperative and interdependent stepsinvolving fractionation, thermal cracking, isomerization and alkylation.

In one specific embodiment the present invention comprises a process forimproving the properties of natural gasoline by fractionating the sameto separate a fraction containing the three carbon atom hydrocarbons andlower boiling constituents, a fraction containing the four carbon atomhydrocarbons, and higher boiling constituents, thermally cracking thethree carbon atom hydrocarbons under controlled conditions to producehigh yields of ethylene, isomerizing the fraction containing the fourcarbon atom hydrocarbons to produce isobutane, and alkylating theisobutane by said ethylene.

The following description and attached diagrammatic drawing illustratingone arrangement of apparatus for carrying out the process of ourinvention, are directed to the preferred type of operation, whichpreferred operation is not necessarily equivalent in results to beexpected with other types of operation. Likewise, although in itsbroadest scope any suitable isomerization and alkylation catalysts maybe employed, the preferred catalysts for both processes are metalhalides and particularly aluminum chloride-containing catalysts whichare utilized in conjunction with hydrogen halides and particularly withhydrogen chloride and which are utilized in a particular method oforxeration wherein the aluminum chloride and hydrogen chloride employed(Cl. 26o-683.4)

in the isomerization step are continuously carried over with thereactants into the alkylation zone, containing a granular packingmaterial, and utilized therein to elect the akylation of the isobutaneby the ethylene.

Referring to the drawing, the charging stock to the process, whichcomprises any natural gasoline or other substantially parainic gasoline,is introduced through line I and valve 2 to stabilizer 3. Since thenatural gasolines available vary considerably with the method of theirrecovery, the exact operating conditions to be employed in stabilizer 3will likewise vary considerably. In

any event, fractionation of the natural gasoline introduced thereto iscontrolled by means of cooling coil 4 and internal reboiler 5 toseparate, as an overhead fraction, the hydrocarbons containing 3 carbonatoms and lighter constituents, a fraction containing the 4 carbon atomhydrocarbons, and higher boiling constituents. In place of cooling coil4, it is within the scope of the invention to employ any other suitablecooling and reiiuxing means, such as recycling a portion of thecondensed overhead distillate. Likewise, in place of internal reboiler5, any other suitable means of introducing the necessary heat may beemployed, such as the use of an external reboiler. These means are wellknown in the art and there is no need for entering into a detaileddescription thereof in this application. It is also within the scope ofthe invention to employ two or three fractionating zones in place of theone stabilizing zone indicated in the drawing.

The gases released in stabilizer 3 are withdrawn from the upper portionthereof lthrough line B and are directed through valve 'I into andthrough condenser 8, the resulting distillate and uncondensed gasespassing through line 9 and valve I0 into receiver 'I I. Since some ofthe conversion products of the process are introduced to stabilizer 3,in a manner to be later described, the products collected in receiver IIwill contain some hydrogen chloride in addition to Vcondensed 3 carbonatom hydrocarbons and other gases. 'I'he exact composition of thematerial collected in receiver II will vary considerably with theconstituents of the natural gasoline charging stock and with theparticular method of operation of the process. In any event, cooling ofthe overhead products fiom the stabilizer is preferably controlled tocondense the three carbon atom hydrocarbons and to leave the hydrogenchloride and other light gases uncondensed. The uncondensed gases andhydrogen chloride are removed from receiver II through line I2 and maybe withdrawn from the process through line I3 and valve I4 to anydesired further treatment.

Preferably all or a portion of this material is4 directed through valvei 5 into hydrogen chloride recovery system I5.

Any suitable hydrogen chloride recovery system may be employed. Since nonovelty is claimed for the particular hydrogen chloride recovery system,there is no need to recite in detail the operation of this step.Regardless of the particular system employed, it is operated to separatethe hydrogen chloride from the other constituents contained therein. Theother constituents may be removed through line I1 and valve I8 tostorage or further treatment as desired, while the hydrogen chloride isremoved from zone I5 through line I9 and valve 20 to pump or compressor2|, by means of which it is directed through line step of the process,which will be subsequently described. Additional hydrogen chloride froman extraneous source may be introduced into line 22 through line 24 andvalve 25.

The distillate collected in receiver II consists essentially of 3 carbonatom hydrocarbons. Due to the limitations of close fractionation inpractical operations, this distillate may contain a minor proportion oflower and higher boiling hydrocarbons. In any event, the distillatecollected in receiver I I is directed therefrom through line 25 andvalve 21 to pump 28, by means of which it is directed through line 29and valve 30 to heating coil 3| in furnace structure 32. The 3 carbonatom hydrocarbons are heated in coil 3| under conditions chosen toeffect a high conversion thereof into ethylene. In general, theseconditions comprise relatively high temperatures and relatively lowpressures. Experiments conducted at 1292 F., 14. pounds per square inch,and a contact time of seconds have yielded 25.5% of ethylene by thethermal conversion of propane. The temperatures employed in this zonewill of course vary, and may range, for example, from 900 F. to 1400 F.at subatmospheric, atmospheric, and slightly superatmospheric pressures.

The products emerging from heating coil 3| are directed through line 33and valve 34 and are cooled by any suitable means, such as heatexchanger 35, to which the cooling medium may be introduced through line36 and valve 31 and withdrawn through line 35 and valve 39. In place ofheat exchanger 35, the heated products may be cooled, for example, bydirect quenching with a suitable cooling medium. The cooled products arewithdrawn from heat exchanger 35 through line 40 and may be directedthrough line 4I and valve 42 into the alkylation step of the system.

The composition of these heat treated products will depend upon thecharacteristics of the distillate collected in receiver and upon theexact operating conditions employed in coil 3|. When the heated productscontain an excessive amount of constituents other than ethylene, it maybe desirable to direct the same through valve 43 and line 44 tofraction-ator 45, preferably equipped with cooling coil 46 and reboiler41 or other suitable cooling and heating means, whereby to separate theproducts therein into lighter gases containing less than two carbonatoms per molecule,

22 and valve 23 to the isomerization-r hydrocarbons containing twocarbon atoms per molecule, unconverted propane, and any heavier productswhich may have been formed in the cracking operation. The lighter gasescontaining less than two carbon atoms per molecule including methane,hydrogen, and the like, may be removed from the process through line 55and valve 49. The hydrocarbons containing two carbon atoms per moleculeare withdrawn from fractionator 45 through line 52 and are directedthrough valve 53 to pump or compressor 54. The

unconverted propane is withdrawn through line 29 to heating coil 3| forfurther conversion into ethylene. In either case, the products suppliedto pump or compressor 54 are directed through line 55, valve 58 andvline 4I to the alkylation stepl of the process. It is a particularfeature of the present invention that the thermally cracked productswill contain high percentages of ethylene which, when utilized in thealkylation of isobutane, as will be subsequently described, produces aiinal alkylate of high octane value.

The fraction containing the four-carbon atom hydrocarbons separated instabilizer 3 will comprise essentially butane and may include minorproportions of lower and higher boiling fractions due to the limitationsof close fractionation in practical operations. The amount of normalbutane and isobutane contained in this fraction will depend upon theconstituents present in the particular charging stock introduced to theprocess. However, the process of the present invention is equallyapplicable to either fractions containing substantially only normalbutane or mixtures of normal butane and isobutane. This fraction iswithdrawn from stabilizer 3 through line 51 and valve 58 to pump orcompressor 59, by means of which it is introduced through line 60 andvalve 6I to isomerization zone 62, together with the hydrogen chloridesupplied thereto through lines 22 and/or 24, as previously described.

In case the charging stock contains oleiinic or other constituents whichmay prove detrimental to the activity of the aluminumchloride-containing catalyst, it is also within the scope of theinvention to pretreat this fraction prior to its introduction intoisomerization zone 62. Any suitable means may be used for this purpose,among which may be mentioned the step of passing th 's fraction througha bed of aluminum chloride or other suitable reagent in a separate zone.A1- ternatively, the aluminum chloride sludge withdrawn through line 69,as hereinafter described, may be utilized for this purpose.

Isomerization zone 52 preferably contains aluminum chloride-containingcatalyst and is operated under conditions whereby isomerization of thenormal butane introduced thereto is effected and at the same timesufilcient aluminum chloride to eilect the subsequent alkylationreaction is carried along with the conversion products leaving thiszone. In general, the temperatures employed in the isomerization zonewhen using aluminum chloride catalyst will range from about to about 250F. and preferably about 185 to about F. The amount of hydrogen chloridecommingled with the butane stream being introduced into theisomerization zone should be sufficient to promote the aluminum chloridecatalyst in order to effect satisfactory isomerization of the normalbutane. In general, this amount may range from about 1.5 to about 5.0

mol per cent or more. We have found that increased amounts of hydrogenchloride are not particularly harmful to the reaction, but that after a.certain maximum the hydrogen chloride4 does not further assist in thereaction. The pressure employed in the isomerization zone is preferablysumcient to maintain liquid phase therein and, in general, will rangefrom about 150 to about 500 pounds or more and preferably from about 210to about 300 pounds.

The products from the isomerization zone which contain isobutane,aluminum chloride and hydrogen chloride, along with other constituents,pass from isomerization zone 62 through line 63 and valve 64 intoalkylation zone 65. The conversion products from the thermal crackingstep are then introduced to alkylation zone 65 by means of line 4|, aspreviously described. Zone 65 preferably contains some sort of granularpacking material such as for example crushed porcelain, preformedporcelain shapes such as berl saddles, pumic, re brick, quartz,activated carbon, diatomaceous earth, raw and acid-treated clays, silicagel, alumina, magnesia, zirconia, titania, composites of silica andalumina and/or zirconia, metals possessing considerable surface such asspongy iron, etc.

The temperature in alkylation zone 65 is preferably controlled to eiectalkylation of the isobutane by the ethylene. In general, thistemperature may range from about 60 F. to about 200 F. or thetemperature maintained in isomerization zone 62 and preferably withinthe ranges of about 90 to about 120 F. We have found that the presenceof paraflinic hydrocarbons other than isobutanewill not greatly affectthe alkylation reaction in zone 65. However, if the total crackedproducts are directed through line 4| to the alkylation zone withoutintervening fractionation, these other paraii'inic gases should beremoved at some step in the process in order to avoid their accumulatingwithin the system. One method of accomplishing this is by removing themin the hydrogen chloride recovery system previously described. Theunconverted propane present in this stream eventually will be recycledby means of lines 26 and 29 to heating coil 3| for further conversioninto ethylene. It is desirable to reduce to a minimum the amount ofpropylene present in the material supplied to the alkylation zone assome alkylation of the isobutane by the propylene will be effected inthis zone and we have found that this tends to reduce the octane valueof the nal alkylated product.

It is essential to have an excess of isobutane present in the alkylationzone. Our experiments have indicated that it is preferable to maintainthe percentage of olens in the alkylation zone to between about 13 andabout 14 percent of the hydrocarbon mixture present therein. Modifiedoperations may permit satisfactory use of a broader range of olefins as,for example, from about to about 15 percent or more. Increased amountsof olens in the alkylation zone tend to undergo polymerization and otherundesirable reactions with a concomitant reduction in the desiredalkylation reaction.

Any suitable means of maintaining the desired temperatures inisomerizatian zone 62 and alkylation zone 65 may be employed. Thesemeans are well known in the art and have been omitted from the drawingin the interest of simplicity. Several obvious methods include thefollowing: (1) Separately heating the butane stream prior tointroduction into isomerization zone 62. (2) Direct heating of theisomerization and alkylation zones. (3) Surrounding the isomerizationand alkylation zones with a bath of suitable heating or cooling medium,as the case may be. (4) Interposing a suitable heat exchanger betweenthe isomerization zone and the alkylation zone to control thetemperature. This method is not as desirable as some of the othermethods as it is preferable to maintain the temperature of the mixtureof the butanes and aluminum chloride until their introduction into thealkylation zone. (5) Controlling the temperature in the alkylation zone,all or in part, by regulating the temperature of the ethylene streamintroduced thereto.

The products from alkylation zone 65 are directed therefrom through line66 and valve 61 to separator 68, wherein the sludge formed in thealkylation reaction is separated from the hydrocarbons. The sludge isremoved through line 69 and may be withdrawn from the process throughvalve 10 for any desired use. This sludge is believed to be an aluminumchloride-hydrocarbon complex and is usually iiuid. It has been foundthat the sludge still retains some activity for inducing the alkylationreaction and it is within the scope of the invention to recycle all or aportion thereof by means of line 1l, valve 12, pump 13, line 14, andvalve 15 to alkylation zone 65. The hydrocarbons separated from thesludge 1n separator 68 are removed therefrom through line 16 and valve11 to pump 18, by means of which they are preferably supplied throughline 19, line and valve 8| to stabilizer 3, although they may beindependently fractionated in accordance with an alternative but notnecessarily equivalent embodiment of the invention. Provision is made inthe case here illustrated for passing all or a portion of thesehydrocarbons in indirect heat exchange with the iinal product of theprocess. 'I'his is accomplished by directing the hydrocarbons throughvalve 82 and through heat exchanger 83, wherefrom they are directedthrough line 84, valve 85 and line 80 to stabilizer 3. In stabilizer 3the alkylated products are commingled with the higher boilingconstituents of the charging stock introduced thereto and the commingledmixture is withdrawn therefrom through line 86, valve 81, heat exchanger83, line 88 and Valve 89.

The following example of one specic operation is given for the purposeof further illustrating the utility of the present invention, althoughnot with the intention of unduly limiting it.

The charging stock comprises a California natural gasoline having an A.P. I. gravity of 74,

and end-boiling point of 325 F. and the following composition:

The charging stock is fractionated to separate the propane and lighterconstituents as an overhead fraction, the propane subsequently separatedby condensation. The propane is cracked at a temperature of 1292 F. anda pressure of 14 pounds .per square inch. The normal butane isisomerizedin the presence of aluminum chloride catalyst at a temperature of about190 F. and under a pressure of about 250 pounds per square inch.Ethylene and unconverted propane from the thermal cracking step arecommingied with the isobutane and the isobutane is alkylated by theethylene at a temperature of about 105 F. under a pressure of 250pounds. The ethylene introduced into the alkylation zone amounts to 14.1percent of the total hydrocarbons therein. Approximately 1.8 mol.percent of hydrogen chloride is commingled with the normal butane priorto isomerization and the hydrogen chloride included with the conversionproducts introduced to the alkylation zone amounts to 1.5 mol percent.The yield of hydrocarbons containing more than carbon atoms per moleculeobtained .from the alkylatlon operation amounts to about 238 percent byweight, based on the olens introduced into the alkylation zone. Thealkylated product, when blended with the normally liquid constituents ofthe natural gasoline in separator 3, produces a iinal gasoline productof satisfactory vapor pressure and of high antiknock value.

We claim as our invention:

1. A process for treating a substantially paranlnic distillatecontaining .propane and normal butane, which comprises separating saidpropane and normal butane from the higher boiling constituents, crackingsaid propane under temperature and pressure conditions adequate toproduce substantial yields of ethylene, isomerizing said normal butaneto isobutane under isomerizing conditions in the presence of a catalysthaving isomerizing and alkylating properties, removing resultantproducts from the isomerizing step together with at least a .portion ofsaid catalyst and commingling therewith ethylene produced in thecracking step, and subjecting the resultant mixture to alkylatingconditions to react isobutane with ethylene in the presence of saidportion of the catalyst.

2. A process for the conversion of natural gasoline which comprisesstabilizing said natural gasoline to separate a fraction containingpropane, a fraction containing normal butane. and a fraction containinghigher boiling constituents, cracking said propane under temperature andpressure conditions adequate to effect conversion thereof intosubstantial yields of ethylene, isomerizing said fraction containingnormal butane in the presence of a catalyst having isomerizing andalkylating properties, removing resultant products from the isomerizingstep together with at least a portion of said catalyst and comminglingtherewith ethylene produced in the cracking step, and subjecting theresultant mixture to alkylating conditions to react isobutane withethylene in the presence of said portion of the catalyst.

3. lA process for the conversion of natural gasoline containing propaneand normal butane which comprises iractionating said natural gasoline inthe presence of conversion products of the process, produced ashereinafter set forth, to separate a fraction containing said propaneand lighter constituents, a fraction containing four carbon atoms permolecule including said normal butane, and a fraction containing thehigher boiling constituents, withdrawing said fraction containing thepropane and lighter constituents, cooling the same to condense saidpropane, separating the condensed propane from the lighter constituents,withdrawing the latter from the process, subjecting said propane tothermal cracking conditions to eiect substantial conversion thereof intoethylene, withdrawing the last mentioned conversion products containingsaid ethylene, unconverted propane and higher and lower boilingconstituents and cooling the same, introducing said fraction containingfour carbon. atoms per molecule, including said normal butane, into anisomerization zone containing an aluminum chloride-containing catalyst,maintaining said isomerization zone under isomerizing conditions,whereby to effect isomerization of said normal butane to isobutane andwhereby to include a portion of said aluminum chloride with theconversion products withdrawn from said isomerization zone, introducingthe last mentioned conversion products including isobutane and saidportion of aluminum chloride into an alkylation zone containing agranular packing material, introducing into said alkylation zone saidconversion products containing said ethylene. maintaining saidalkylation zone under temperature and pressure conditions whereby toeiect alleviation of said isobutane by said ethylene in the presence ofsaid portion of aluminum chloride, withdrawing the products from saidalkylation zone and introducing the same into a separating zone whereinthe hydrocarbons are separated from aluminum chloride-containingproducts, withdrawing the latter from the process, and fractionatingsaid last mentioned hydrocarbons in the presence of said naturalgasoline as previously set forth.

4. A process such as deiinedin claim 3 wherein hydrogen chloride iscommingled with said fraction containing four carbon atoms per moleculeprior to the isomerization of said normal butane.

5. A process such as defined in claim 3 wherein hydrogen chloride ispassed successively through said isomerization zone, said alkylationzone and said separating zone into said fractionation zone. to bewithdrawn therefromin commingled state with said fraction containing thepropane and lighter constituents, and wherein said hydrogen chloride isrecovered from said lighter constituents and the recovered hydrogenchloride is commingled with said fraction containing four carbon atomsper molecule prior to the isomerization of said normal butane.

6. A process such as defined in claim 3 wherein at least a portion ofsaid aluminum chloridecontaining products separated from thehydrocarbons is returned to said alkylation zone.

'7. A process such as dened in claim 3 wherein said propane is crackedat a temperature oi' from about 900 to about 1400 F.

8. A process such as dened in claim 3 wherein said isomerization iseffected at a temperature of from about 160 to about 250 F. under a.pressure of from about to about 500 pounds per square inch.

9. A process such as defined ln claim 3 wherein said alkylation iseffected at a temperature of from about 60 to about 200 F. under apressure of from about 150 to about 500 pounds.

10. A process for the conversion of natural gasoline containing propaneand normal butane which comprises fractionating said natural gasoline inthe presence of the conversion products of the process, produced ashereinafter set forth, to separate a fraction containing said propaneand lighter constituents, a fraction containing four carbon atoms permolecule including said normal butane, and a fraction containing thehigher boiling constituents, withdrawing said fraction containing thepropane and lighter constituents, cooling the same to condense thepropane, separating the condensed propane from the lighter constituents,withdrawing the latter from the process, heating said propane to atemperature of from about 900 to about 1400 F. whereby to eectsubstantial conversion thereof into ethylene, withdrawing the lastmentioned conversion products containing said ethylene, unconvertedpropane and higher and lower boiling constituents and coolingthe same,introducing said fraction containing four carbon atoms per molecule,including said normal butane, into an isomerization zone containingaluminum chloride-containing catalyst and maintained at a temperature offrom about 185 to about 195 F. under a. pressure of from about 210 tovabout 300 pounds per square inch, whereby to effect isomerization ofsaid normal butane to isobutane and whereby to include a portion of saidaluminum chloride with the conversion products withdrawn from saidisomerization zone, introthe presenceof said natural gasoline aspreviously set forth.

11. A process as dened in claim 10, wherein said conversion productscontaining said ethylene, unconverted propane and higher and lowerboiling constituents are fractionated to s eparate said ethylene fromsaid unconverted propane and said higher and lower boiling constituents,said ethylene being introduced to said alkylation zone, said unconvertedpropane being recycled to said heating for further conversion intoethylene, and said higher and lower boiling constituents being withdrawnfrom the process.

12. A process for treating parainic distillate containing propane andnormal butane which comprises fractionating the distillate to separatetherefrom a propane-containing fraction and a butane-containingfraction, -cracking the ilrstducing the last mentioned conversionproducts,

including isobutane and said portion of aluminum chloride, into analkylation zone containing a granular packing material, also introducinginto said alkylation zone the conversion products containing saidethylene, maintaining said alkylation zone at a temperature of fromabout 90 to about 120 F. undera pressure of from about 210 to about 300pounds per square inch, whereby to eect alkylation of said isobutane bysaid ethylene in the presence of the said portion of aluminum chloride,withdrawing the products from said alkylation zone and introducing thesame into a separating zone wherein the hydrocarbons. are separatedfromaluminum chloride-containing products, withdrawing the latter from theprocess, and fractionating said last mentioned hydrocarbons in namedfraction to convert propane to ethyl ene,subjectingthesecond-mentionedfractionto isomerization in the presence ofaluminum chloride to convert normal butane into isobutane, removing fromthe isomerizing step a reaction mixture containing isobutane and atleast a portion of said aluminum chloride and commingling therewithethylene produced in the cracking step, and subjecting the commingledmaterials to alkylating conditions to react isobutane with ethylene inthe presence chloride.

13. The process as dened in claim 12 further characterized in thathydrogen chloride is supplied to the isomerizing step and transferredtherefrom to the alkylating step.

v14. The process as dened in claim 12 further characterized in that saiddistillate comprises natural gasoline.

CHARLES G. DRYER. RALPH B. THOMPSON.

rof said portion of the aluminum

